1. Field of the invention.
The present invention relates to devices for sensing the level of oil in oil sumps in hermetic refrigeration and air conditioning compressors, such as scroll, reciprocating or rotary types, and more particularly to devices for optically inspecting and automatically sensing the level of oil in sumps. One aspect of the present invention relates to sight glass type devices attached to the housing of a compressor for allowing a person to visually examine the interior of the compressor from outside the compressor housing to determine the level of oil in an oil sump or to examine the surface of oil in a sump. Another aspect of the present invention relates to automatic sensing devices that optically sense the presence or level of oil in an oil sump and perform some desired function, such as alarm or service indication or compressor shut down, in the event the oil level becomes critically low.
2. Description of the related art.
The most common form of oil level sensing device utilized today and in the past in hermetic compressors is the mechanical float switch. A float is supported by oil in the sump of a compressor and with the oil at an acceptable level the switch maintains contact between a power source and the compressor. Should the oil, and the float supported thereby, drop below a threshold level, then the switch interrupts the power supply to the compressor and thereby terminates operation. A problem associated with magnetic float switches is that they generally utilize a magnetic reed switch which attracts metallic debris that binds the float switch and causes the device to become inoperable resulting in unnecessary compressor shut down or the loss of compressor protection. This type of device is wholly mounted internal the compressor housing requiring costly compressor disassembly to replace a malfunctioning switch.
Sight glass instruments have been incorporated in hermetic compressors to permit visual inspection of the level or presence of oil in a sump. Such sight glass instruments require an operator to periodically examine the compressor to verify that an acceptable level of oil is present in the sump. A problem with such sight glass instruments is that usually compressors are mounted in the interior of an outer housing of other devices, such as refrigerators, air conditioners, automobiles, etc., and, even if positioned most favorably, are difficult to examine and may require some disassembly. Another problem with such devices is that in the event of sudden catastrophic loss of oil in a sump, no advance warning is given and damage occurs without the opportunity for remedial measures.
Automatic oil level sensing devices are known which are generally mounted wholly in the interior of a compressor housing and electrically connected to the compressor power source via electrical leads which extend from the interior of the housing to the outside of the housing through a hermetic outlet in the housing. Typically, the leads are connected to the power source external of the compressor housing. When the sensor determines that the level of oil in the sump has dropped below a critical threshold level, the sensor, via switching contacts, relay contacts, TTL logic, etc., automatically interrupts the delivery of power to the compressor and operation is terminated. One problem with such known sensors is that the only way to verify the existence of a fault condition is to disassemble the compressor, no visual inspection is provided.
Often it is the sensor that has failed and has erroneously terminated compressor operation when in fact a sufficient level of oil is present in the sump. Again, the only way to determine this is to disassemble the compressor unless a second device, such as a sight glass described above, is also incorporated in the compressor. However, if the sensor has in fact failed then it is still necessary to disassemble the compressor to replace the failed sensor. This is not an economically desirable option but the only other alternative is to electrically bypass the failed sensor and permit unprotected compressor operation.
A problem with externally mounted sensors is that the sensor continues to sense an acceptable oil level after having fallen off or been removed from the sight glass. This situation may lead to damage to the compressor if the oil level does become low.